Abbildungen der Seite

These trials were made at the works of obtained are free from all question which Messrs. Nasmyths, Gaskell, and Co., Patri might otherwise arise as to the capability croft, near Manchester. They were con of the boiler, or the quality of fuel made ducted in the presence of a member of their use of. firm, of their superintendent, Mr. Wilson, The two engines, being thus supplied with and of two of the patentees of the Disc En steam under identical circumstances, were gine.

employed, on alternate days, to drive the The object proposed being to ascertain, same fans at similar velocities. with the utmost possible accuracy, the re It was found, by previous trials, that with lative quantities of water as steam, and, con the quantity of steam the boiler would consequently, of fuel, which would be required veniently produce, the Disc afforded a greater to enable each engine to perform the same amount of power than the Reciprocating amount of work, it was a matter of the first Engine ; therefore the number of fans driven, importance to determine upon some work their velocity, and the discharge of air, were which would oppose an uniform resistance. so adjusted as to provide for the resistance after much consideration, I selected that being within the capability of the latter enwhich is presented by fans revolving at high gine; and thus I was enabled to keep the velocities; considering that these machines, fans revolving at a very uniform relocity when driven at an uniform rate of motion, throughout both trials. This velocity was would offer a resistance so nearly invariable accurately indicated by a counting apparatus as to satisfy this primary condition. The connected with an intermediate sbaft beChristmas holidays fortunately admitted of tween the engine shaft and the fans. fans being appropriated entirely for this The two engines were of the non-conpurpose, so that no extraneous circumstance densing class, and discharged their steam interfered to change the nature, or amount, into the atmosphere. of the work during the trials.

For the registration of the water a res. The Reciprocating Engine was made by sel was provided, which was found to conMessrs. Nasmyths, Gaskell, and Co. It is tain 338 lbs. by weight; and it was arranged a beam engine, thoroughly well constructed, for the whole of the water used during the in excellent condition, and in every respect trials to be measured by means of this res. unexceptionable as a specimen of its class. sel; and the boiler being furnished with a I found the diameter of the cylinder to be glass gauge, I endeavoured to have the same 145 inches; the length of stroke 2 feet, pressure of steam, and the same quantity of 21 inches ; and the number of double strokes water in the boiler, at the conclusion, as at of the piston, during the trial, averaged the commencement of each experiment. In 41% per minute.

this I succeeded within a variation of an The Disc Engine (called 16 horses' power) inch in the level of the water, for which dae I found to have a steam chamber of 27 allowance was made. inches in diameter, and the mean number of The weight of coal burnt during each trial revolutions effected, during its trial, was was also accurately ascertained; the fire at 118} per minute. With these proportions, the conclusion being, as nearly as possible, and at these respective speeds, the volume of in the same state as at the commencement. steam which should pass through each of the Having thus taken the precautions I contwo engines in a given time, as defined by sidered requisite to obtain results worthy of the transit of the parts on which the steam confidence, and having made some prepara. acts, is very nearly the same; an equality tory trials with each engine, the fans were which must be considered as tending to sa connected with the Reciprocating Engine tisfy doubts as to the results of the trials and they were driven without intermission having been affected by any other circum for six hours. During this time the quanstances than those strictly arising out of the tity of water as steam which passed through principles on which the two engines are con the engine was 10,406 lbs., equal 1734} lbs. structed.

per hour ; and the coal consumed was 20 Both engines were alternately supplied cwt., equal 373} lbs. per hour ; the evapowith steam from the same boiler. This I ration being in the low ratio of 43 lbs. of found to be very deficient in the extent of water for i lb. of coal. The counter ac. surface exposed to heat, and the setting was tuated by the intermediate shaft registered ill arranged; consequently, the proportion during this trial 14,301, the greatest difof water evaporated for the coal consumed ference in the velocity of the fans during any was low; but, as I adopted on this, as on hour being about 6 per cent., and the mean former occasions, the mode which is con speed of the engine 41:6 strokes per minute. sidered to afford the only accurate means of On the following day the fans were conascertaining the expenditure of steam for a nected with the Disc Engine and driver for given effect, viz., that of determining the 5 hours and 57 minutes, when the counter,

ntion of water as steam, the results connected as before, had registered 14,318,

[blocks in formation]


being 17 more than on the previous day ; the greatest difference in the velocity of the fans during any hour being little more than I per cent. The quantity of water as steam required to supply the engine was 8,697 lbs., equal 1449 lbs. per hour ; and the coal con-, sumed was 16 cwt., equal 2984 lbs. per hour; the evaporative ratio being about 47 lbs. of water for 1 lb. of coal. The mean number of revolutions of the engine shaft per minute was 118).

Immediately after the conclusion of this trial, the fans were again connected with the Reciprocating Engine, and the same velocity being given to them, an indicator diagram was taken off which, by comparison with the diagrams of the preceding day's trial, showed that the resistance overcome by the Disc Engine, was somewhat greater than by the Reciprocating Engine, but the difference was very small,

In order to ascertain the amount of effective power exerted by the Disc Engine, I availed myself of Mr. Davies' Dynamometer, The principle of this very complete instru. ment is, that the force of the resistance taken on the periphery of a driving drum or toothed wheel on the engine shaft, is denoted on the dial-plate of a spring balance, so placed that its index may be easily observed whilst the engine is at work. The engine being stopped, standard weights are suspended from the drum or wheel until the index of the spring balance marks the same degree at which it stood on the dial-plate during the action of the engine; and the velocity and circumference of the drum or wheel in feet being also known, true data are obtained for determining the work perform, ed. By means of this apparatus—which I consider to be worthy of the utmost con. fidence-I found the mean resistance, or load, actually overcome, to be equal to 17

Although this instrument was applied only to the Disc Engine, yet as it defined the resistance overcome by each, it indicated with equal truth, the effective power exerted by the Reciprocating Engine. The Dynamometric observations were further corroborated by the diagrams obtained on applying the ordinary indicator to the Reci. procating Engine, when driven without a load and when performing the same work. The indicator was verified by comparing the pressures marked by this instrument with those of a mercurial gauge acted upon by steam at various densities. The quantity of water as steam required by the Reciprocating Engine being 1734} lbs. per hour, and the effective power exerted equal to 17 horses, the water consumed is in the ratio of 102 lbs. for each horse power, per hour; and the water required by the Disc Engine being

1449 } lbs. per hour, this is in the ratio of 85+ lbs. per horse power per hour. Thus, the consumption of steam, and consequently of fuel, for equal effect, by the Reciprocating, is upwards of 19 per cent. greater than by the Disc Engine.

The mean pressure of steam in the cylinder of the Reciprocating Engine, as exhibited by the indicator diagrams, was equal to 254 lbs. per square inch, and the mean pressure in the chamber of the Disc Engine, as exhibited by a mercurial gauge constantly connected with it, was 23+ lbs. per square inch.

The above effects were obtained by the two Engines when working unexpansively and with steam at comparatively low pressures. As regards non-condensing Reciprocating Engines, I have not previously met with any (and I have conducted experiments, similar to the foregoing, on many engines of this class) which has required less than 120 lbs. of water as steam per horse power per hour, even when using steam at high pressure, a fact which establishes the excel. lence of the Reciprocating Engine subjected to trial, as it only consumed 102 lbs. per horse power per hour.

The results of these trials are thus exhibited in terms of the quantity of water as steam actually expended in overcoming the same resistance by the two engines, and, also, according to the conventional phrase of horse power ; but that quantity was greater in both cases than would have been required, had the steam pipes and cylinders been coated. Though, however, these were uncovered and a considerable quantity of steam must have been condensed, which had no share in producing the effect, the relative results are unaffected by this circumstance, as I found, that a nearly equal extent of surface (about 45 square feet) was so exposed in both cases.

When experiments of this kind are conducted in a manner liable to little error, evidence of their accuracy will arise from independent sources, and we possess direct means of verifying the correctness of the principal results obtained, viz., that the Reciprocating required 19 per cent. more steam than the Disc Engine, for equal effect.

The counter informed us that the Reciprocating Engine made in the 6 hours 149781 double strokes, which multiplied into its capacity* (passages, &c. included) gives a total of 78,7264 cubic feet, as the volume of steam which passed through the cylinder at the absolute pressure of 40 lbs. per square inch. The ratio of the volume of water contained in that steam is as 1 to 677.

horses' power.

The passage equalled 0.405 cubic feet.-Total capacity, 0,256 cubic feet.

The capacity of the Disc Engine* was also exactly ascertained; it was filled and evacuated 42,3223 times during the 5 hours and 57 minutes; and the total volume of steam expended amounted to 69,535} cubic feet, having a mean absolute pressure of 38 lbs. per square inch, for which the ratio of the elementary water is as 1 to 710. By comparing the quantities of water given by this method of computing the respective consumption of each engine, it appears that the Reciprocating would necessarily require 184 per cent. more water than the Disc Engine, which confirms the correctness of the two experiments.

There are still a few points which I feel called upon to note, as they affect, to a certain extent, the results of the trials.

The Disc Engine was quite new, and therefore its acting surfaces were not in that high state of polish I have seen in those which have been in constant use for many months. Thus somewhat more power would be consumed in overcoming its own friction in this case, than in older engines. On the contrary, the Reciprocating Engine had been at work for a period which had brought its rubbing surfaces into a perfect state. The Disc Engine, also, was planted, temporarily, on the wood floor of an upstairs room being simply bolted down to sleepers; and the manner in which the driving strap was obliged to be rigged, for the purpose of the trial, increased the friction of the engine shaft on one journal. Though the practi. cability of such an arrangement exhibits a property of much importance to the ema ployers of engines, viz., the small mass and cost of foundation necessary for the Disc Engine, yet, it is unquestionable that the cir. cumstances referred to were adverse to this engine in a comparison as respects economy.

I have already alluded to another circumstance which was adverse to the economy of both engines, viz., the surface of steam pipe, and &c. exposed to the influence of the air in the building, and amounting to about 45 square feet. By experiments on a large scale, and pursued for a lengthened period, which I have made with steam under similar circumstances, and at similar pressures to those used on this occasion, I have found that 1 square foot of cast-iron pipe will condense fully 1 pound of steam per hour. Thus, about 270 lbs. of water should be respectively deducted from the consumption of the Disc and Reciprocating Engines, as those quantities had no share in the production of the effect. Making this deduction, it comes out that the effective horse power was really obtained with 82% lbs. of water

as steam, per hour, by the Disc Engine, and with 99lbs. by the Reciprocating Engine.

In concluding this statement of the results attending an investigation alike interesting and valuable, as regards the practical facts elicited, I must express my entire confidence in their accuracy, checked as my observations were throughout by so many competent persons, all of whom were most diligent in guarding against error during both trials. I am not acquainted with any experiment in which the same load, without the slightest change in any part of the intermediate gear. ing, has been made the medium of deciding on the comparative merits of different steam engines; and had I to choose again, I do not think a resistance could be selected subject to so little variableness as the fans adopted on this occasion. This kind of resistance offers peculiarly accurate means of noticing the quantity of irregularity occurring in the speed of any engine. The uniform velocity obtained by the Disc Engine was very apparent, and struck me as a property of no small importance as regards its application to various purposes, for which an equable rate of motion is a desideratum. I am, Gentlemen, your obedient servant,

(Signed) Josiah PARKES. 12, Great College-street, Westminster,

February 3, 1842. P. S. In compliance with a suggestion of the patentees, I have visited several of the Disc Engines on which I made a series of experiments in January of last year; I have, also, communicated with all the gentlemen employing these engines which then came under my notice. The engines referred to have now been working upwards of eighteen months, and in addition to my own percep. tion that they are in perfect order, I am informed, in reply to my applications, that they have been in operation with constant regularity, also that the cost of repairs during the above period, had been so trifling as to be unworthy of mention.

J. P.


Sir,-- With this


will receive a rough model of an instrument used in the north of England in hay-making, and which they call a hay sweep. The description that accompanies the model is, I think, sufficiently clear for any rough carpenter or wheelwright to make one by, and the cost of the one I saw was only 258. The machine from which I made this model was drawn by two horses, which were driven by two men, whọ, each placed onę

• Disc capacity, 1.643 cubic feet.

THE DISC ENGINE AND CAPTAIN CARPENTER'S PROPELLERS. 329 foot where the letter B is, and another the right, and the other to the left, to foot on the rope to keep it down, and guide their horses ; but I think, if there guided the horses with long reins. To was a sufficient weight attached to, or keep themselves steady, they rested their fixed on each end, that there would be arms on the top rail, one looking to no occasion for any one to stand there ;

[merged small][graphic][ocr errors][subsumed][subsumed][subsumed][ocr errors]

the horses might then be led by even two through holes, thereby affixing the wings boys.

to the centre. These iron bars should I think this would be an exceeding be round. useful machine in all moderately level A strong rope is interlaced through pastures, and, although it has been used the rails near to the bottom, and that is for many years in the north of England, connected with the top by a smaller rope ; I never saw it elsewhere.

and at each end is a splinter bar A a, I remain, Sir, your obedient servant, to which a horse is affixed.

M. S. R. This machine is of great service in Description.

catching weather, when your hay is nearly This machine should be made of oak, made, and when to prevent its being wetted except where the uprights, a a a a, by sudden rain, you wish to get it up in are, and those (four) should be of iron; large cocks. The present plan to acthe bottom parts, with flat or round complish this, is by the men pushing it heads, let in neatly, so that the bottom up with forks, but by the machine should be quite level, and the tops fasten more may be got up in one hour than ed by screws and nuts.

many men would be able to do in a day. The top and bottom rails are 4 inches Where the rick is made in the same by 3, or 14 inches circumference. Length field, or in one of several hay fields of the back or centre part 8 feet; ditto adjoining each other, the time and trouof each side or wing 4 feet 6 inches ; ble of carting is saved, for, by this machine depth all round, 3 feet 6 inches. The it may be drawn up at once to the place two sides, or wings, are so fixed as to where the rick is to be made, and only move backwards or forwards by turning two horses are required. on the outward iron bars, which pass

THE DISC ENGINE AND CAPTAIN CARPENTER'S PROPELLERS. We noticed some time ago the scientific tation, which was in progress, to the pinnace arrangements adopted in the fitting out of of the vessel, of one of the well-known disc the steam frigate Geyser, and also the adap engines and of the steam propellers invented

by the commander of the Geyser, Capt. Car cluding paragraph of his " description," be penter. The advantage expected from having evidently has not yet mastered its modus the pinnace thus equipped was, that she might operandi. be able to tow the other ships' boats, against Mr. Tozer (page 315) endeavours to prove wind and tide, into shallow barbours and rivers a want of novelty, by bringing forward the where an armed force might be wanted, but contrivance of a Mr. Wood. Mr. Walker's which the vessel herself could not, from her Belgian patent was at first refused in condraught of water, penetrate. Two trials of this

sequence of a supposed resemblance between auxiliary pinnace steamer were made last his contrivance, and that of Mr. Wood; on week on the Thames, in the presence of Sir examination, however, the two inventions Edward Parry, Comptroller of Her Majesty's were found to be dissimilar, and the patent Steam Marine, and Messrs. Ewart and was passed. Lloyd, the Government Engineers, and the It is not at all probable, if this excellent result, as reported to us, was in the highest mode of raising water had been once hit degree satisfactory. The pinnace is 30 feet upon, that it would ever have been lost, in length, 9 feet wide, and is capable of though we are told, by the by, that the carrying 8 tons. She is remarkably bluff in thing is a "perfect fallacy;" so saith Mr. the bows, and therefore not adapted for high A. Emslie, at page 315. velocities ; but power (a little power only) That it is perfect, I will not assert; that and not velocity, is what is aimed at in the it is no fallacy has been incontrovertibly present instance. The disc engine with proved. I have watched the progress of this which she is fitted weighs altogether but 6 invention from its first germ to its present cwt., and measures 3 feet by 1 foot 6 ; leav maturity, and Mr. E. might have been coning ample space for a full complement of tented to take my description, or to bring men. The connexion between the engine against it the result of some practical expeand the propellers (of which we gave a full riment. Mr. Emslie says, “ The lift does description in our No. 844, p. 18) by means not discharge the water, and upon that of grooved pulleys, and catgut bands. Dur reasoning he builds his hypothesis of the ing the first trial, a regular speed of 7 miles similarity of Mr. Walker's engine to a lift per hour through the water was obtained, as

and force pump.

The fact is, the lift des indicated by Massey's log, although from discharge the water ! This is seen plainly the unfavourable shape of the boat, a wave enough in filling Mr. Walker's glass eleta. of nearly 18 inches deep was carried before tors; it is also shown by naking the doen the bows. The velocity of the engine-shaft stroke so slowly as to be inoperatire

, Eben was 200 revolutions a minute, and more than the up stroke performs its own peculiar that is not, we understand, desired from office. The fact is also shown by filling the the propelling shafts. In the second trial, the elevators, and removing them from the pinnace drew after her at about the same rate water in the well cistern, or what-not," of speed, a regular gun-boat, furnished with when their contents are still delivered with. cannon, and a complement of fifty men, with out any aid from the “consequent resist. their arms and ammunition. The engine and boiler are so fitted to the pinnace, that they Mr. Emslie further says, “I defy Mr. can be taken out in five minutes, and replaced Baddeley to show that this weight of water ready for operations in the same brief space is in any way counterbalanced by the other of time.

elevator, while in action." Mr. Emslie's defiance will not induce me to undertake the

part of showman ; but Mr. Walker bes WALKER'S HYDRAULIC ENGINE.

shown to thousands, and, I dare say, will

show to thousands more, that which Mt. Sir,-Walker's hydraulic engine is de Emslie cannot comprehend. The mode of servedly attracting great attention, and the demonstration resorted to by Mr. Walker, better it is understood, the more it will be is simply to detach one of the elevators from admired. Your last Number (975) contains the beam ; on working the machine, the three papers, in two of which Mr. Walker's quantity of water then raised is just one invention is adverted to rather disparaging. half, but the labour is nearly doubled! 01 ly. The first is a rival, (S. P.,) who favours refixing the elevator, and working the ma. us with a modification of the powder puff chine, the quantity of water is doubled, and pump” of the sixteenth century.

the labour reduced as before, affording the spiral wire, tube of mackintosh cloth, or of most unequivocal proof of the advantages leather," bespeak the ephemeral character of of the equilibrium to which I alluded in such a machine, and stand little chance with your 971st Number. a competitor which threatens to last almost Mr. Emslie may depend upon it there is for ever—and a day. “S. P." has seen more in Mr. Walker's hydraulic engine than Mr. Walker's machine, but from the con was ever dreamed of in his philosophy, and


" The

« ZurückWeiter »